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Date: Thu, 28 May 2020 11:37:19 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Adrian Hunter <adrian.hunter@...el.com>
Cc: Jiri Olsa <jolsa@...hat.com>, Andi Kleen <ak@...ux.intel.com>,
linux-kernel@...r.kernel.org,
Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCH 1/2] perf record: Respect --no-switch-events
Em Thu, May 28, 2020 at 03:08:58PM +0300, Adrian Hunter escreveu:
> Context switch events are added automatically by Intel PT and Coresight.
> Make it possible to suppress them. That is useful for tracing the
> scheduler without the disturbance that the switch event processing
> creates.
>
> Example:
>
> Prerequisites:
>
> $ which perf
> ~/bin/perf
> $ sudo setcap "cap_sys_rawio,cap_sys_admin,cap_sys_ptrace,cap_syslog,cap_ipc_lock=ep" ~/bin/perf
> $ sudo chmod +r /proc/kcore
>
> Before:
>
> $ perf record --no-switch-events --kcore -a -e intel_pt//k -- sleep 0.001
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.938 MB perf.data ]
> $ perf script -D | grep PERF_RECORD_SWITCH | wc -l
> 572
>
> After:
>
> $ perf record --no-switch-events --kcore -a -e intel_pt//k -- sleep 0.001
> Warning:
> Intel Processor Trace decoding will not be possible except for kernel tracing!
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.838 MB perf.data ]
> $ perf script -D | grep PERF_RECORD_SWITCH | wc -l
> 0
>
> $ sudo chmod go-r /proc/kcore
> $ sudo setcap -r ~/bin/perf
Thanks, tested as root and applied.
- Arnaldo
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> ---
> tools/perf/Documentation/perf-record.txt | 4 +++-
> tools/perf/arch/arm/util/cs-etm.c | 3 ++-
> tools/perf/arch/x86/util/intel-pt.c | 3 ++-
> tools/perf/builtin-record.c | 5 +++--
> tools/perf/util/record.h | 6 ++++++
> 5 files changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
> index 561ef55743e2..97b1a866ab22 100644
> --- a/tools/perf/Documentation/perf-record.txt
> +++ b/tools/perf/Documentation/perf-record.txt
> @@ -458,7 +458,9 @@ This option sets the time out limit. The default value is 500 ms.
>
> --switch-events::
> Record context switch events i.e. events of type PERF_RECORD_SWITCH or
> -PERF_RECORD_SWITCH_CPU_WIDE.
> +PERF_RECORD_SWITCH_CPU_WIDE. In some cases (e.g. Intel PT or CoreSight)
> +switch events will be enabled automatically, which can be suppressed by
> +by the option --no-switch-events.
>
> --clang-path=PATH::
> Path to clang binary to use for compiling BPF scriptlets.
> diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
> index 607499b41bea..cea5e33d61d2 100644
> --- a/tools/perf/arch/arm/util/cs-etm.c
> +++ b/tools/perf/arch/arm/util/cs-etm.c
> @@ -265,7 +265,8 @@ static int cs_etm_recording_options(struct auxtrace_record *itr,
> ptr->evlist = evlist;
> ptr->snapshot_mode = opts->auxtrace_snapshot_mode;
>
> - if (perf_can_record_switch_events())
> + if (!record_opts__no_switch_events(opts) &&
> + perf_can_record_switch_events())
> opts->record_switch_events = true;
>
> evlist__for_each_entry(evlist, evsel) {
> diff --git a/tools/perf/arch/x86/util/intel-pt.c b/tools/perf/arch/x86/util/intel-pt.c
> index fdb917fcf511..3fc547769707 100644
> --- a/tools/perf/arch/x86/util/intel-pt.c
> +++ b/tools/perf/arch/x86/util/intel-pt.c
> @@ -779,7 +779,8 @@ static int intel_pt_recording_options(struct auxtrace_record *itr,
> * Per-cpu recording needs sched_switch events to distinguish different
> * threads.
> */
> - if (have_timing_info && !perf_cpu_map__empty(cpus)) {
> + if (have_timing_info && !perf_cpu_map__empty(cpus) &&
> + !record_opts__no_switch_events(opts)) {
> if (perf_can_record_switch_events()) {
> bool cpu_wide = !target__none(&opts->target) &&
> !target__has_task(&opts->target);
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 02d85f4e4517..dc6d5ba2fff8 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -2490,8 +2490,9 @@ static struct option __record_options[] = {
> "Record namespaces events"),
> OPT_BOOLEAN(0, "all-cgroups", &record.opts.record_cgroup,
> "Record cgroup events"),
> - OPT_BOOLEAN(0, "switch-events", &record.opts.record_switch_events,
> - "Record context switch events"),
> + OPT_BOOLEAN_SET(0, "switch-events", &record.opts.record_switch_events,
> + &record.opts.record_switch_events_set,
> + "Record context switch events"),
> OPT_BOOLEAN_FLAG(0, "all-kernel", &record.opts.all_kernel,
> "Configure all used events to run in kernel space.",
> PARSE_OPT_EXCLUSIVE),
> diff --git a/tools/perf/util/record.h b/tools/perf/util/record.h
> index dce6332f5071..84dbbc3f0204 100644
> --- a/tools/perf/util/record.h
> +++ b/tools/perf/util/record.h
> @@ -36,6 +36,7 @@ struct record_opts {
> bool record_namespaces;
> bool record_cgroup;
> bool record_switch_events;
> + bool record_switch_events_set;
> bool all_kernel;
> bool all_user;
> bool kernel_callchains;
> @@ -77,4 +78,9 @@ extern struct option *record_options;
>
> int record__parse_freq(const struct option *opt, const char *str, int unset);
>
> +static inline bool record_opts__no_switch_events(const struct record_opts *opts)
> +{
> + return opts->record_switch_events_set && !opts->record_switch_events;
> +}
> +
> #endif // _PERF_RECORD_H
> --
> 2.17.1
>
--
- Arnaldo
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